Method to estimate tire-road friction, prior to safety systems engagement
Technical solutions are described for estimating tire-road friction in a vehicle pro-actively, prior to safety systems of the vehicle are engaged. An example method includes computing a slip for the vehicle based on one or more wheel speeds, acceleration, and tire pressure measurement. The method further includes determining a slope (α) as indicator of tire-road friction for the vehicle based on the acceleration and the slip. Further, the method includes sending the slope to an autonomous controller of the vehicle for adjusting vehicle kinematics according to the estimated friction using the slope.
1. A method for estimating tire-road friction in a vehicle proactively, prior to safety systems engagement, the method comprising:
computing a slip for the vehicle based on one or more wheel speeds, acceleration, and tire pressure measurement, wherein the slip is a longitudinal slip computed as
ω
R
-
V
V
during braking, and as
ω
R
-
V
ω
R
during acceleration, where V is a vehicle speed, ω is the wheel speed and R is the effective wheels radius based on the tire pressure measurement and the vehicle's weight;
determining a slope (α) as indicator of tire-road friction for the vehicle, the slope (α) being based on the acceleration and the slip; and
causing an autonomous controller of the vehicle to adjust vehicle kinematics according to the slope (α).
2. The method of claim 1 , wherein determining the slope comprises determining a slope of a line on a plot for the acceleration vs slip, the line being drawn on the plot from the origin to a point represented by present values of the acceleration and the slip.
3. The method of claim 1 , further comprising, notifying an operator of the vehicle based on the slope prior to the safety system being engaged.
4. The method of claim 1 , further comprising, sending the slope to a controller.
5. The method of claim 1 , further comprising, sending the acceleration vs slip to a server computer to warn other vehicles about surface friction.
6. The method of claim 1 , further comprising, indicating a tire-health to an operator of the vehicle based on the slip, the tire-health being deteriorated in response to the slip vs acceleration being below a predetermined safety threshold.
7. A system for proactively estimating tire-road friction in a vehicle, prior to engagement of a safety system of the vehicle proactively, the system comprising:
one or more sensors;
an autonomous controller configured to maneuver the vehicle autonomously; and
a friction processor coupled with the one or more sensors, and the autonomous controller, the friction processor configured to:
compute a slip for the vehicle based on one or more wheel speeds, acceleration, and tire pressure measurement, wherein the slip is a lateral slip is computed as:
-
arctan
∫
a
y
dt
∫
a
x
dt
,
where a y is the lateral acceleration, and a x is the longitudinal acceleration;
determine a slope (α) as indicator of tire-road friction for the vehicle based on the acceleration and the slip;
causing the autonomous controller of the vehicle to adjust vehicle kinematics according to the slope (α); and
indicate a tire-health to an operator of the vehicle based on the slope, the tire-health being deteriorated in response to the slope being below a predetermined safety threshold.
8. The system of claim 7 , wherein determining the slope comprises determining a slope of a line on a plot for the acceleration vs the slip, the line being drawn on the plot from the origin to a point represented by present values of the acceleration and the slip.
9. The system of claim 7 , wherein the autonomous controller is further configured to send the slope and a weight of the vehicle to a second controller associated with a second vehicle.
10. The system of claim 7 , the autonomous controller further configured to send the slope and a weight of the vehicle to a server computer to warn other vehicles about the tire-road friction.
11. A vehicle controller for proactively estimating tire-road friction in a vehicle, prior to engagement of a safety system of the vehicle proactively, the vehicle controller configured to:
compute a slip for the vehicle based on one or more wheel speeds, an acceleration, and a tire pressure measurement;
determine a slope (α) as indicator of tire-road friction for the vehicle based on the acceleration and the slip;
adjust, autonomously, vehicle kinematics according to the slope (α);
estimate a road surface type based at least in part on the slope (α);
determine a condition of at least one tire of the vehicle based at least in part on the slope (α); and
broadcast, by the vehicle controller using an inter-vehicles communications network, the road surface type to one or more neighboring vehicles.
12. The vehicle controller of claim 11 , wherein the slip is a longitudinal slip computed as
ω
R
-
V
V
during braking, and as
ω
R
-
V
ω
R
during acceleration, where V is a vehicle speed, ω is the wheel speed and R is the effective radius of the wheel based on the tire pressure measurement and estimation of the vehicle's weight.
13. The vehicle controller of claim 11 , wherein the slip is lateral slip that is computed as:
-
arctan
∫
a
y
dt
∫
a
x
dt
,
where a y is the lateral acceleration, and a x is the slip.
14. The vehicle controller of claim 11 further configured to send the slope and weight of the vehicle to a server computer to warn other vehicles about the tire-road friction.
15. The vehicle controller of claim 11 further configured to indicate a tire-health to an operator of the vehicle based on the slope, the tire-health being deteriorated in response to the slope being below a predetermined safety threshold.